Today, cell phones are used by a number of people, even teenagers. For example, high school students often carry cell phones provided by their parents so that they may make or receive emergency phone calls. However, problems often arise when a student receives non-emergency phone calls from friends at inopportune times, for example, while the student is attending a class. Such phone calls can be disruptive to the student and to the student's classmates.
Therefore, it would be advantageous to have a method for restricting calls to a cell phone, such that a cell phone user will not be disturbed when non-emergency phone calls are placed to his or her cell phone at inopportune times, but will be alerted when emergency phone calls are placed to the cell phone.